Tvheadend

Just started to get the errors below doing apt-get update on Ubuntu 20.04.6 LTS - been running TVH and updating successfully via this repo for over a year, and haven't changed anything

Get:3 http://apt.tvheadend.org/stable focal InRelease
Err:3 http://apt.tvheadend.org/stable focal InRelease
Clearsigned file is not valid, got 'NOSPLIT' (does the network require authentication?)
Reading package lists... Done
E: Failed to fetch http://apt.tvheadend.org/stable/dists/focal/InRelease Clearsigned file is not valid, got 'NOSPLIT' (does the network require authentication?)
E: The repository 'http://apt.tvheadend.org/stable focal InRelease' is no longer signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

Edited to add:

this is the package that came with the repo, I haven't compile it myself

SW version: 4.2.8-36~g5bdcfd8ac
API version: 19
Name: Tvheadend
Capabilities: caclient tvadapters satip_client satip_server trace libav
Tuner: Silicon Labs Si2168 #0 : DVB-T #0
Signal Strength: 0
uuid: 9d4a4f7871619bfe1f20aed122474f6d

I am about to update Ubuntu to 22.04 but wanted to sort this out first. to Thanks in advance for any guidance.